Method for improving the handling characteristic of a vehicle during emergency braked driving

ABSTRACT

The invention relates to a method for improving the handling characteristic of a vehicle during partially braked driving. The invention is characterized by a driving stability regulation device for correcting or regulating deviations from a desired lane, said device being configured in such a way that the start and the conclusion of an activated regulation situation is carried out depending upon conditions which are detected in accordance with straight-ahead driving conditions and cornering.

TECHNICAL FIELD

The invention relates to a method for improving the handlingcharacteristic of a vehicle during partially-braked driving.

BACKGROUND OF THE INVENTION

For several years, cases have already been known in which vehicles of aprototype series tend to exhibit critical driving behavior in thepartially-braked area. This effect, whose causes may include theelastic-kinematic properties of the vehicle, can lead to a decrease indriving comfort and even to critical situations, if the conditions areunfavorable. Moreover, in general, every vehicle, due to differentvertical forces and friction values or friction pairing in the brake(different coatings), an asymmetric generation of longitudinal forceportions can occur in the partially-braked area. These forces may resultin a yaw moment causing uncomfortable even critical driving behavior ofthe vehicle.

Vehicles with such a chassis or brake configuration influence thedriving behavior during the braking process to the effect that thevehicle does not stay in the desired driving lane during the brakingprocess. The vehicle follows a course which is determined by the chassisand/or brake configuration. In this case one speaks of the “pulling” ofthe vehicle. This pulling may, represent a stable driving status, but itnevertheless deviates from the driver's intention. Using the methodswhich have been used to date to optimize the braking process one can,however, not compensate for such a behavior. ABS (anti-lock brakesystem), for example, a regulation of individual wheels influences thebraking in a wheel brake as a function of the driving behavior of thiswheel. The electronic brake force distribution (EBD), which is containedin the ABS, automatically regulates the brake pressure of the back axleand it keeps the vehicle stable with the best possible braking of theback axle. EBD adapts the brake force of the back wheels to the forcesof the front wheels and thus prevents both underbraking and alsooverbraking of the back wheels. EBD uses the components of the ABS forthe pressure modulation of the back wheel brakes, for each individualwheel.

Using this method, however, moments about the vertical axis of thevehicle cannot be generated, because the wheels in each case arecontrolled only individually after the brake skidding, but not as afunction of the vehicle course.

In addition, there is no correction of the state by an ESP (electronicstability program), because the conditions trigger an ESP interventionand the regulation thresholds are reached too late, or not at all. TheseESP conditions and regulation thresholds could also not be changed orlowered appropriately, because the required interference distance forincorrect regulations must be maintained.

If there is an ESP intervention, which, in cases of unstable drivingconditions, generates an additional yaw moment, which acts against theturning of the vehicle to compensate for the turning of the vehicleabout the vertical axis by increasing or decreasing the brake pressureindividually in a wheel brake, changes in delay occur, which areobserved by the driver. Additional drawbacks are the filling of the lowpressure reservoir during the pressure decrease, as well as the openingof the reversing valve during the activated pressure increase, and theassociated filling of the low pressure absorbers, which can be felt inthe brake pedal. In addition, in the braking pressure range, where theregulation or adjustment of the brake device occurs, switchable orificefor the inlet valves can be switched, which leads to pressure increasegradients which differ from the pressure increase gradients ofswitchable orifices which are not switched.

Furthermore, in the case of a partially-braked (still no ABS activity)driving in a curve with a motor vehicle, in particular after the firstoccurrence of vehicle instabilities due to oversteering, which requiresteering actions by the driver for stabilization, which may exceed thedriver's capacities. The primary causes for this behavior are the shiftof the wheel load toward the front axle, which tends to move thecapacity for lateral force transfer to the front. As a result, thedescribed tendency to oversteering occurs. In principle, this effect canbe supported by the following boundary conditions:

-   -   a) brake status (use of a portion of the transferable force        already for the braking force)    -   b) unfavorable, already statically present, axle load        distribution toward the front axle (tends to occur more with        front-drive vehicles)    -   c) vehicles with back axle drive, because most of the drag        moment of the motor in the superposed push status shifts the        back axle slightly into a skidding status which in turn requires        a portion of the transferable lateral force potential.

The mentioned instabilities associated with oversteering occurparticularly in the braking status, because, as a result of the brakeforce distribution in this area, no yaw moment is transferred to thevehicle structure, to counteract the oversteering tendency. If, on theother hand, the driver continues to increase the brake pressure, thenhe/she reaches the non-positive limit in the tire/pavement system and,as a result, the ABS is activated. Because the transferable force on theside located within the curve is smaller due to the conferred transversedynamics, the yaw moment is generated, which acts against theoversteering tendency. Therefore, the stability problems of the vehicleare usually eliminated, as soon as the driver applies excessive brakepower in the partially-braked area.

For systems, which are intended to achieve vehicle stabilization in thementioned partially-braked area, there is thus the possibility of usinga pressure modulation similar to the one obtained with activated ABS,namely an activated pressure decrease at the curve-interior wheels,already in the partially-braked area. In principle, this is alreadyachieved with the known ESP function. However, the ESP regulationpresents the following drawbacks:

-   -   a) The ESP regulator is too insensitive (start thresholds too        high) for oversteering disturbances, which tend to accumulate in        the lower dynamic range (the result is an insufficient effect).    -   b) An uncomfortable overall impression is produced (often        activated pressure increase is required with the associated        valve and pump activity has a negative effect on pedal and noise        comfort).    -   c) Through the ESP function indicator lamp, the driver also        receives an additional return message in the case of        interventions which merely represent driver assistance.

Therefore, it would be desirable, independently of the cause whichresults in a deviation from the desired driving course, to provide amethod or a regulation which, by targeted interventions of the brakingsystem, reduces the yaw motion of the vehicle for any path and at anyspeed to a degree which is comfortable for, or easily controllable by,the driver.

In EP 0 482 374 A1, an electro-pneumatic brake device for commercialvehicles and buses is described, which presents an electrical brakeencoder as well as an electrical control device, which is equipped forprocessing brake signals and also for processing the signals of sensorsignals of a steering system. In the case of a control, effected by thebrakes, of the pressure control values which precede the brakecylinders, to remove by regulation the steering moments, the steeringsensor signals should also be taken into account. In the process, thebraking device determines the correction pressures exclusively in thecase of straight-ahead driving.

BRIEF SUMMARY OF THE INVENTION

The invention is based on the problem of providing a method to improvethe handling-characteristic of a vehicle during partially-brakeddriving.

According to the invention, this problem is solved by a method toimprove the handling characteristics of a vehicle duringpartially-braked driving, by designing a driving stability regulationfor the correction or regulation of deviations from a desired drivinglane in such a manner that the start of an activated regulationsituation and the exit from an activated regulation situation occur as afunction of conditions, which are determined depending on whetherstraight-ahead driving or cornering conditions occur.

By the method, a regulation situation is recognized as a function ofwhether the vehicle is driving straight ahead or in a curve. It is onlyafter the regulation situation has been recognized that the deviationfrom the desired driving lane of the vehicle during the braking processis determined and that the deviation between the desired driving laneand the lane through the vehicle moves is corrected, as a function ofthe result of the determination, if the deviation exceeds at least athreshold value. It is preferred to carry out the method in a vehiclewith ESP driving stability regulation, so that the threshold value canbe a modified ESP threshold value. The method allows a reliabledetection of the driving situation which is to be changed on the basisof the deviation of the ESP vehicle model, in a new range. Here, anindependent ESP regulator with more sensitive thresholds and anintervention strategy without activated pressure increase is used. Thepump activation is avoided almost completely and no ESP function lightis activated. Thus, the regulator has the property of acting earlier andto a large extent without the driver noticing it. During the entireregulation activities, the driver thus advantageously does not receiveany haptic, optical or acoustical return messages (pedal, lamp, signaltone).

Additional advantages of the low dynamic ESP (LDE) method are:

-   -   Robustness against incorrect detections or disturbances.    -   Optimized valve activity with the goal of actuation control as        needed.    -   Selective pump actuation only in case it is needed (inclusion of        the low pressure reservoir model).    -   Harmonic interaction with other subsystems such as ESP, ABS, EBD        and ESBS.

The method advantageously presents the following steps: determination ofinternal and external magnitudes and statuses which represent thehandling characteristics and the driving in lanes of the vehicle,determination of an activated regulation situation or of the start of aregulation as a function of straight-ahead driving conditions orcornering, taking into consideration the internal and externalmagnitudes and statuses, and correction or regulation of deviations froma desired driving lane by setting or modifying the adjusted brakingpressure, when at least one threshold value has been exceeded, which isdetermined as a function of rotation about the vertical axis of thevehicle.

Advantageously, the low dynamic ESP (LDE) is used to provide a methodwhich, independently of the cause of the pulling of the vehicle, reducesthe yaw motion of the vehicle, by means of targeted interventions on thewheel-brakes of the brake system, at any speed, to a level which can becontrolled by the driver.

It is advantageous to compare the internal and external magnitudes withthreshold values, and to carry out an evaluation of the statuses,regardless of whether the statuses of the vehicle stability regulationare activated or not activated.

To determine the start or end of a regulation situation, it isadvantageous to take into account, as internal and external magnitudesand states, the steering angle (δ), the steering angle speed (δ), thebraking pressure (p_(main)), the vehicle speed (ν), the lateralinclination angle (α), the lateral acceleration (α_(actual)), the radiusof curvature and the regulation statuses of a vehicle stabilityregulation.

The threshold value, which is determined based on the rotation about thevertical axis of the vehicle, and which must be exceeded for thecorrection or regulation of deviations from a desired driving lane bysetting or modifying the adjusted braking pressure, is determinedadvantageously based on the straight-ahead driving conditions orcornering. Advantageously, the threshold value (S_(ESP)) of an ESPdriving stability regulation is formed according to ESP drivingstability-criteria and modified, in the case of straight-ahead drivingconditions using a first correction factor, and in the case of corneringusing a second correction factor (k_(STRAIGHT 1) k_(CURVE 2)).

As conditions for the detection of the start of a regulation situation,it is provided that, in the case of partially-braked straight-aheaddriving conditions, the start G_(in) of the regulation occurs accordingto the relation G_(in)=ƒ(δ, {dot over (δ)}, p_(main), ν, α), if one ormore of the following conditions are satisfied.

-   -   ESP is not activated.    -   ABS is not activated.    -   Straight-ahead driving conditions have been detected.

Furthermore, as additional advantageous condition for the detection ofthe start of a regulation situation, it is provided, that in the case ofpartially-braked straight-ahead driving, the start of the regulationoccurs, if several of the following conditions are satisfied:δ<k degree, δ<k ₁ degree/s, p _(main) <k ₂ bar, ν<k ₃ km/h,α<k₄ degree,

-   -   with the threshold values k to k₄.

As additional conditions for the detection of the start of a regulationsituation, it is provided that, in the case of partially-brakedcornering, the start K_(in) in the regulation occurs according to therelation K_(in)=ƒ(δ, δ, p_(main), ν, a, α_(actual)) if one or more ofthe following conditions are satisfied:

-   -   Curve has been detected    -   Curve radius>k₁₀ m, preferably >20 m    -   Oversteering has been detected    -   ESP is not activated    -   ABS is not activated.

In the case of partially-braked cornering, a start of the regulationpreferably occurs if several of the following conditions are satisfied:δ<f(ν) degree, δ<k ₅ degrees, p _(main) >k ₆ bar, ν>k ₇ km/h,α<k ₈ degree, α_(actual) >k ₉ m/s²,with the threshold values k₅ to k₉ and ƒ(ν). The steering angle mustfall below a threshold value, which is formed as a function of thespeed. Empirical examinations here lead to three steering anglethreshold values, which were in the range between 2 and 30 degree, andwhich were associated with vehicle speeds in the ranges 30 to 50 km/h,100 to 140 km/h and 220 to 250 km/h.

As a condition for the detection of the end of a regulation situation itis provided that, in the case of partially-braked straight-ahead drivingconditions, the end of corrective regulation of deviations from adesired lane occurs by setting or modifying the adjusted brakingpressure, if at least one of the following conditions is satisfied

-   -   ESP is activated    -   ABS is activated    -   δ>k₁₁ degree,    -   δ>k₁₂ degrees,        with the threshold values k₁₂ and k₁₁.

If the start conditions (activated regulation situation) are satisfied,but partially-braked straight-ahead driving conditions occur withtermination of the activated regulation situation, without a correctionor regulation of deviations from a certain driving lane having occurred,at least one of the following additional conditions must be satisfied:

-   -   δ>k degree,    -   δ>k₁ degree,    -   p_(main)<k₂ bar,    -   ν<k₃ km/h,    -   α>k₄ degree,        straight-ahead driving conditions have not been detected.

As a condition for the detection of an end of a regulation situation, itis provided, that in the case of partially-braked cornering, the end ofthe corrective regulation of deviations from a desired driving laneoccurs by setting or modifying the adjusted braking pressure, if atleast one of the following conditions is satisfied:

-   -   ESP is activated    -   ABS is activated    -   δ>k₁₂ degrees.

If the start conditions (activated regulation situation) have beensatisfied, but partially-braked cornering occurs with termination of theactivated regulation system, with a corrective regulation of deviationsfrom a desired lane having occurred, at least one of the followingadditional conditions must be satisfied:

-   -   δ>ƒ(ν), that is the steering angle is greater than a threshold        value which is dependent on the vehicle speed, with linear        interpolation between these reference places    -   δ>k₁₃ degrees,    -   p_(main)<k₁₄,    -   optionally as a function of the lateral acceleration    -   ν<k₁₅ km/h,    -   α>k₁₆ degree,    -   α_(actual)<k₁₇ m/s²,    -   curve radius<k₁₇ m, preferably <20 m    -   ESP is not activated, {ESP situation detection detects no        cornering (constant or delayed)}    -   t_(p)>k₁₈ s,    -   with threshold values k₁₃ to k₁₈ and ƒ(ν).

It is advantageous that no change in the adjustment of the brakingpressure occurs if the following conditions have not been satisfiedfirst:

-   -   ESP is not activated;    -   ABS is not activated;    -   Straight-ahead driving conditions have been detected.

The brake interventions, which are caused by the road stabilityregulation for the corrective regulation of deviations from the desireddriving lane, advantageously occur by setting or modifying the adjustedbraking pressure via a longitudinal force reduction by decreasing thepressure on at least one curve-interior wheel, preferably on thecurve-interior back wheel. An advantageous variant of the LED methodprovides for the pressure decrease to occur on both curve-interiorwheels.

While the set pressure difference on the front axle is compensated afterthe end of the regulation, the pressure difference which has been builtup by the electronic brake force distribution (EBD) at the rear axleremains even after the regulation.

An embodiment example of the invention is represented in the drawingsand described in greater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawing:

FIG. 1 shows a vehicle with ESP regulation system;

FIG. 2 shows a status device which clarifies the activated or notactivated regulation situations: partially-braked cornering,partially-braked straight-ahead driving conditions, and no regulationsituation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a vehicle with ESP regulation system, brake device, sensorsand communication possibilities, in a schematic representation. The fourwheels bear the reference numerals 15, 16, 20, and 21. On each of thewheels 15, 16, 20, 21, a wheel sensor 22, 23, 24, 25 is provided. Thesignals are applied to an electronic control unit 28, which determines,based on predetermined criteria, the vehicle speed v [sic; ν] from therpm values of the wheels. Furthermore, a yaw rate sensor 26, atransverse acceleration sensor 27 and a steering wheel angle sensor 29are connected with the component 28. In addition, each wheel presents anindividually controllable wheel brake 30, 31, 32, 33. These brakes areoperated hydraulically and they receive pressurized hydraulic fluidthrough the hydraulic lines 34, 35, 36, 37. The braking pressure is setvia a valve block 38, where the value block is controlled by electricalsignals, independently of the driver, which signals are generated in theelectronic control unit 28. Via a main cylinder which is actuated by abrake pedal 39, the driver can request the application of a brakingpressure in the hydraulic lines. The pressure sensors P are provided inthe main cylinder and the hydraulic lines, respectively, by means ofwhich the driver's intent to brake is detected. Via an interface (CAN),the electronic control unit is connected to the motor control unit.

Via the ESP regulation system with brake device, sensory system andcommunication possibilities, which presents the equipment elements

-   -   four wheel rpm value sensors    -   pressure sensor (braking pressure in the main cylinder p_(main))    -   lateral acceleration sensor (lateral acceleration signal        α_(actual), lateral inclination angle α)    -   yaw rate sensor ({dot over (ψ)})    -   steering wheel angle sensor (steering angle δ, steering angle        speed {dot over (δ)})    -   individually controllable wheel brakes    -   hydraulic unit (HCU)    -   electronic control unit (ECU)        a statement concerning the current driving situation can be        obtained, and thereby an activated or not activated regulation        system can be implemented via the start and end conditions. This        allows the implementation of a main component of the LDE (low        dynamic ESP) behavior, namely the driving situation detection,        while the other main component, the interaction with the brake        system, also makes use of the essential components of the ESP        regulation system. In the situation detection, the ESP sensory        system and the resulting measured and derived, internal and        external, signal magnitudes are used to make a decision whether        a typical driving situation for the LDS exists. Furthermore,        verification is carried out to determine whether other partial        systems of the ESP, or the ESP itself, already intervene via the        brake system on the wheel brakes 30 to 33. In this case, the LDE        regulation system remains passive, that is no regulation        intervention occurs via the LDE process. The detection of the        driving situation is based on the large steering angle (δ),        steering angle speed ({dot over (δ)}), brake pressure        (p_(main)), vehicle speed (ν), lateral inclination angle (α),        lateral acceleration (α_(actual)), curve radius and the statuses        of the ESP road stability regulation ESP activated, ABS        activated, ESP not activated, ABS not activated, and,        optionally, other functions such as, for example, those of        hydraulic brake system. In the process, an activated or not        activated regulation situation is determined as a function of a        partially-braked straight-ahead driving condition and a        partially-braked cornering. The structure of the status device        is represented in FIG. 2. It has, as statuses, the control        situations, LDE with partially-braked straight-ahead driving        conditions and LDE with partially-braked cornering, as well as        the rest situation “no regulation situation.” Each arrow in the        diagram characterized a permissible status transition. This        transition becomes activated, when the start and end conditions        for a given regulation situation are satisfied. As a result of        the unequivocal formulation and assignment of the regulation        situations in a status device, no overlap between the function        areas, or ambiguities can occur, and all the transitions also        occur only in the prescribed form. As soon as one of the two        activated LDE regulation situations has been reached, the        post-connected LDE regulator is given the permission to start        the regulation to correct or regulate the deviations from the        desired driving lane. Because only one control situation occurs        at that time, the same LDE regulator can be used for both        statuses, that is the properties of the regulator can be changed        as a function of this situation (for example start delay times,        start and/or end thresholds (optionally also by means of a        transverse acceleration-dependent projection)). The conditions        for the transitions between statuses “LDE no regulation”>“LDE        partially-braked straight-ahead driving conditions” and vice        versa (start and end conditions) are described in greater detail        below. In case of partially-braked straight-ahead conditions,        several of the following conditions, preferably all, must be        satisfied for an activated regulation situation (start): ESP is        not activated, ABS is not activated, straight-ahead driving        conditions have been detected,        δ<k degree, δ<k ₁ degrees, p _(main) >k ₂ bar, ν>k ₃ km/h,        α<k₄ degree        using the threshold values k to k₄, which are determined        empirically.

The end of the activated control situation, with a corrective regulationof the deviation from a desired driving path, occurs if at least one ofthe conditions is satisfied:

-   -   ESP is activated    -   ABS is activated    -   δ>k₁₁ degree,    -   δ>k₁₂ degrees,    -   with threshold values k₁₁ and k₁₂.

If only one activated regulation situation occurs, without correction orcontrol of the deviation from the desired driving path (LDE notactivated), then the end of the activated regulation situation occurs,if at least one of the conditions is satisfied:

-   -   δ>k degree    -   δ>k₁ degree/s,    -   p_(main)<k₂ bar,    -   ν<k₃ km/h,    -   α>k₄ degree,        straight-ahead driving conditions have not been detected.

In driving tests, it has been shown that the LDE regulator, for theregulation situation LDE in case of partially-braked cornering, requiresmore sensitive start thresholds than for the regulation situation LDE incase of partially-braked straight-ahead driving conditions. Below, theconditions for the transitions between the statuses “LDE no regulationsituation” and “LDE partially-braked corner” are described. Theconditions which are mentioned below for the start of the regulationsituation “LDE partially-braked cornering” should preferably all besatisfied simultaneously (rounding off).

In partially-braked cornering, for the start of regulation to occur,several, preferably all, of the following conditions must be satisfied:

a) Standard ESP is not activated

b) ABS is not activated

c) Steering angle δ is smaller than the threshold value (as a functionof the vehicle speed [δ<ƒ(ν)]), preferably three steering anglethreshold values=(between 2 and 30 degrees) for the threespeeds=(between 30 and 50 km/h, 100 and 140 km/h, 220 and 250 km/h) withlinear interpolation between these reference values

d) steering angle speed {dot over (δ)} is smaller than the thresholdvalue k₅

e) a driver applied preliminary pressure p_(main) is greater than thethreshold value k₆, which can optionally be formed as a function of thetransverse acceleration

f) vehicle speed ν is greater than the threshold value k₇

g) transverse inclination value α of the driving lane is smaller thanthe threshold value k₈

h) transverse acceleration α_(actual) is greater than the thresholdvalue k₉

i) curve radius is grater than a threshold value k₁₀, preferably 20 m

j) ESP situation detects cornering (constant or delayed)

k) time after the beginning of the braking does not exceed a certainlimit, preferably 3 seconds

For the precise formulation of the conditions b), different advantageousprocedures are proposed. One possibility consists in allowing the startto occur only if, in general, the function ABS is activated at no wheel15, 16, 20, 21. Furthermore, it would be possible to activate only if,at a given wheel, where the LDE wants to apply brake pressuremodulation, the ABS function is not yet activated. It would also bepossible to allow pressure modulation by LDE at an axle only if the ABSis not yet activated at the same axle.

In the case of partially-braked cornering, the end of the correction orregulation of deviations from a desired driving lane by setting ormodifying the adjusted braking pressure occurs, if at least one of thefollowing conditions is satisfied (one condition alone being satisfiedis sufficient):

-   -   a) Standard ESP is activated    -   b) ABS is activated    -   c) Steering angle speed {dot over (δ)} is greater than the        threshold value k₁₂ degree(s)

For the condition b), the above described conditions apply again.Provided the LDE regulator has not yet carried out a correction orregulation of a deviation from the desired driving lane, the conditionslisted below apply, in addition to a) through c), for the end of theregulation situation to occur (for example, the case is possible wherethe start conditions of the regulation situations were satisfied, butlater the regulation deviation which remains to be described fell belowthe start threshold of the LDE), where one of the following conditionshas to be satisfied to end the activated regulation situation; [[.]]

-   -   l) steering angle δ is greater than a threshold value (ƒ(ν)),        which is dependent on the vehicle speed, preferably three        steering angle threshold values=(between 2 and 30 degree) for        the three vehicle speed=(between 30 and 50 km/h, 100 and 140        km/h, 220 and 250 km/h) with linear interpolation between these        two reference places)    -   d) steering angle speed {dot over (δ)} is greater than a        threshold value k₁₃ degree/s    -   e) driver applied pressure p_(main) is smaller than the        threshold value k₁₄, which can optionally be formed as a        function of the lateral acceleration    -   f) vehicle speed ν is smaller than a threshold value k₁₅ km/h    -   g) lateral inclination value α of the driving lane is greater        than a threshold value k₁₆ degree    -   h) lateral acceleration α_(actual) is smaller than a threshold        value k₁₇ m/s²    -   i) curve radius is smaller than a threshold value k₁₇        (preferably 20 m).    -   j) ESP situation detection detects no cornering (constant or        delayed)    -   k) time t_(p) after the beginning of the braking exceeds a        certain threshold value k₁₈ seconds

If the driving situation has been detected unequivocally, then theregulation can be carried out. As regulation magnitude, one uses the yawrate {dot over (ψ)} of the vehicle here, whose deviation from the modeldesired behavior represents a measure of the deviation from the desireddriving lane, which is to be reduced to a minimum. In comparison to theESP yaw rate regulation, with the LDE, the intervention occurs alreadyat substantially smaller deviations from the regulation. For thispurpose, the ESP regulation threshold (S_(ESP)), which is formed basedon ESP road stability criteria, is modified by the ESP road stabilityregulation, in the case of straight-ahead driving conditions by means ofa first, and in the case of cornering by means of a second, correctionfactor (k_(STRAIGHT 1) k_(CURVE 2)).

In contrast to the conventional ESP regulation, in which the additionalyaw moment (see DE 195 15 059 A1) is controlled by an activated pressureincrease at the curve-exterior front wheel, with the Low Dynamic ESP(LDE) the stabilization of the vehicle occurs via longitudinal forcereduction by pressure decrease at the curve-interior wheels. Noactivated pressure increase occurs. The selective pump control, which isused here and which functions only to prevent overfilling of thelow-pressure reservoir, and the minimization of the value controlssubstantially improve the comfort level. The LDE activities can thusbarely be perceived by the driver, so that the ESP function light alsodoes not need to be switched on.

LDE interventions, as a rule, are designed similarly to ESP oversteeringinterventions. However, the pressure decrease in the LDE occurssimultaneously at both curve-interior wheels, where the main focus is onthe possible decrease at the rear axle.

While the pressure difference which is set at the front axle iscompensated after the end of the regulation, the pressure differencewhich has been built up at the rear axle by EBD persists even after theregulation.

The above mentioned decreases are applied as a function of the dynamicsand the extent of the pulling. In addition, the LDE contains a number ofmeasures to prevent unjustified regulations due to brief and permanentsignal disturbances or incorrect detections.

To optimize the transitions from the LDE to the ESP, in view ofachieving a more comfortable regulation, the start thresholds of the ESPare broadened, so that an ESP intervention occurs only in case ofgreater instabilities, which cannot be compensated by pressure decreasealone.

1. Method to improve the handling characteristic of a vehicle in case of partially-braked driving, characterized by a driving stability regulation to correct or regulate deviations from a desired driving lane, which is designed in such a manner that the start of an activated and the end of an activated regulation situation occurs as a function of conditions which are determined based on straight-ahead driving conditions and cornering.
 2. Method according to claim 1, with the steps of detection of internal and external magnitudes and statuses, which represent the vehicle status parameters and the lane driving of the vehicle, detection of an activated regulation situation or the start of a regulation as a function of a straight-ahead driving condition or cornering, taking into account the internal and external magnitude and statuses, and correction and regulation of deviations from a desired driving lane by setting or modifying the adjusted braking pressure, when at least one threshold value is exceeded, which is determined based on the rotation above the vertical axis of the vehicle.
 3. Method according to claim 1 or 2, characterized in that the internal and external magnitudes are compared with threshold values, and an evaluation of the statuses occurs in such a manner that a determination is made whether the statuses of driving stability regulation are deactivated or not activated.
 4. Method according to claim 1, characterized in that the internal and external magnitudes and statuses, the driving angle (δ), the driving angle speed ({dot over (δ)}), the braking pressure (p_(main)), the vehicle speed (ν), the transverse inclination angle (α), the transverse acceleration (α_(actual)) the curve radius and regulation statuses of a vehicle stability regulation [sic].
 5. Method according to claim 1, characterized in that the threshold value is determined based on the straight-ahead driving condition or cornering.
 6. Method according to claim 3, characterized in that the threshold value of an ESP driving stability regulation is formed based on ESP driving stability criteria, and the threshold value (S_(ESP)), in case of a straight-ahead driving condition, is modified by means of a first, and, in case of cornering, by means of a second correction factor (k_(STRAIGHT 1) k_(CURVE 2)).
 7. Method according to one of claims 1 to 4, characterized in that in the case of a partially-braked straight-ahead driving conditions, the start G_(in) of regulation occurs based on the relation G_(in)=ƒ(δ, {dot over (δ)}, p_(main), ν, α) if one or more of the following conditions are satisfied: ESP is not activated ABS is not activated Straight-ahead driving conditions have been detected.
 8. Method according to claim 7, characterized in that, in case of a partially-braked straight-ahead driving condition, the start of regulation occurs, if several of the following conditions are satisfied: δ<k degree, δ<k ₁ degree/s, p _(main) <k ₂ bar, ν<k ₃ km/h, α<k₄ degree, with the threshold values k to k₄.
 9. Method according to one of claims 1 to 4, characterized in that in partially-braked cornering, the start Kin of regulation occurs according to the relation K_(in)=ƒ(δ, δ, p_(main), ν, α, α_(actual)), if one or more of the following conditions are satisfied: Curve is detected Curve radius>k₁₀ m, preferably >20 m Oversteering not detected ESP is not activated ABS is not activated
 10. Method according to claim 9, characterized in that, in partially-braked cornering, the start of the regulation occurs, if several of the following conditions are satisfied: δ<f(ν) degree, δ<k ₅ degrees, p _(main) >k ₆ bar, ν>k ₇ km/h, α<k ₈ degree, α_(actual) >k ₉ m/s², with the threshold values k₅ to k₉ and ƒ(ν).
 11. Method according to one of claims 1 to 5, characterized in that, in partially-braked straight-ahead driving, the end of the correction or regulation of deviations from a desired driving lane occurs by setting or modifying the adjusted braking pressure, if at least one of the following conditions is satisfied ESP is activated ABS is activated δ>k₁₁ degree, δ>k₁₂ degree/s, with the threshold values k₁₂ and k₁₁
 12. Method according to claim 11, characterized in that during partially-braked straight-ahead driving, the end of the activated regulation separation occurs, without any correction or regulation of deviations from a desired driving lane having occurred, if at least one of the following addition conditions is satisfied: δ>k degree, δ>k₁ degree/s, p_(main)<k₂ bar, ν<k₃ km/h, α>k₄ degree, Straight-ahead driving conditions have not been detected.
 13. Method according to one of claims 1 to 4 or 6, characterized in that, during partially-braked cornering, the end of the correction or regulation of deviations from a desired driving lane by setting or modifying the adjusted braking pressure occurs, if at least one of the following conditions is satisfied: ESP is activated ABS is activated δ>k₁₂ degree/s.
 14. Method according to claim 12, characterized in that during partially-braked cornering the end of the activated regulation situation occurs, without a correction or regulation of deviations from a desired driving lane having taken place, if at least one of the following additional conditions is satisfied: δ>ƒ(ν), that is the steering angle is greater than a threshold value which is dependent on the vehicle speed, with linear interpolation between these reference place δ>k₁₃ degree/s, p_(main)<k₁₄, optionally as a function of the transverse acceleration ν<k₁₅ km/h, α>k₁₆ degree, α_(actual)<k₁₇ m/s², Curve radius<k₁₇ m, preferably <20 m ESP is not activated, {ESP situation detection detects no cornering (constant or delayed)} t_(p)>k₁₈ s, with the threshold values k₁₃ and k₁₈ and ƒ(ν).
 15. Method according to one of claims 1 to 13, characterized in that no setting or modification of the braking pressure occurs, if the conditions according to claims 7, 8 or 9, 10 have not been satisfied first.
 16. Method according to one of claims 1 to 10, characterized in that, the correction or regulation of deviations from the desired driving lane by setting or modifying the adjusted braking pressure occurs via a longitudinal force reduction by pressure decrease on at least one curve-interior wheel, preferably on the curve-interior back wheel.
 17. Method according to claim 15, characterized in that the pressure decrease occurs on both curve-interior wheels.
 18. Method according to one of claims 1 to 16, characterized in that the pressure difference which is set by the pressure decrease at the rear axle by the electronic brake force distribution (EBD) is maintained. 